Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as “braces”. Braces comprise a variety of appliances such as brackets, bands, archwires, ligatures, and O-rings. After they are bonded to the teeth, periodic meetings with the orthodontist are required to adjust the braces. This involves installing different archwires having different force-inducing properties or by replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces are effective, they are often a tedious and time consuming process requiring many visits to the orthodontist's office. Moreover, from a patient's perspective, they are unsightly and uncomfortable. Consequently, alternative orthodontic treatments have been developed. A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such appliances comprise a thin shell of elastic material that generally conforms to a patient's teeth but is slightly out of alignment with the initial tooth configuration. Placement of the elastic positioner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances comprising new configurations eventually moves the teeth through a series of intermediate configurations to a final desired configuration. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,873, assigned to the assignee of the present invention, and incorporated by reference for all purposes.
In addition to their ease of use, polymeric positioning appliances are generally transparent, providing an improved cosmetic appearance, and impart substantial force on the teeth, due to stiffness of the appliance. Each aligner shell has an inner shape that is configured to move the patient's teeth to the next planned position. However, when a patient's teeth do not follow this planned movement by not moving or moving in an unplanned direction, a “lag of movement” occurs. When this lag of movement becomes too great, that is, when the difference between the current position of the patient's teeth and the planned position at which the aligner is to move the teeth becomes too great, in many cases, the aligner is no longer able to be snapped onto the patient's teeth. Accordingly, improved appliances and techniques are needed to reduce this lag in movement during orthodontic treatment, and to reduce unwanted tooth movements.
The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted.